<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>边框</title>
    <style>
        #d1 {
            width: 200px;
            height: 200px;
            background-color: aqua;
            border: 2px double red;
            /* 设置圆角 */
            border-radius: 100px;
        }
        #d2 {
            width: 200px;
            height: 100px;
            background-color: blueviolet;
            border: 2px double red;
            /* 设置圆角 */
            border-radius: 50px;
        }
        #d3 {
            width: 200px;
            height: 100px;
            background-color: greenyellow;
            border: 2px double red;
            /* 设置圆角 */
            border-radius: 100px/50px;
        }
    </style>
</head>
<body>
    <div id="d1"></div>
    <div id="d2"></div>
    <div id="d3"></div>
</body>
</html>